Work Limits: Only the general areas shown on the project maps is where beaver dam analogs (BDAs) are to be constructed. Exact BDA locations will be flagged and identified by the government prior to work beginning. The project manager and contractor will identify an estimated start date for work to begin on the project. The project manager will provide the contractor with a notice to proceed once conditions are suitable to initiate work. Upon receiving the Notice to Proceed, the Contractor shall promptly enter the project area, locate BDA locations, and begin construction of BDAs. Definition of BDA unit: A BDA unit is essentially 2 square feet of BDA materials including one wood post, tree branch, and other fill material, and the coconut fiber biodegradable blanket. A BDA unit will be defined as one, 2-4” diameter untreated wood post being driven into the creek bed approximately 2’ deep or until it is solid enough that it won’t be knocked over by the current water flow at the time of construction. With 2’ of willow or similar branch material laying horizontal on the ground, woven between posts, stacked, and compacted so that water can barely spill through to a height of 2’ above the streambed. 4’ in width of biodegradable coconut fiber should be placed to help catch sediment as well. This would be placed at the crest of the dam and laid down to extend along the creek floor to prevent the water from undercutting the dam. Lastly, mud or rocks should be placed at the bottom and edges of this coconut fiber so that water does not flow through underneath the dam and undercut it but instead will flow over the top of the dam and in the middle. Once this is complete, this will be considered one BDA unit. Bids should be made according to this BDA unit. However, this does not constitute a completed BDA and for the BDA unit to be counted the BDA must span the entire stream bank and hold water so that the water is flowing over the top in the middle of the dam. The BDA unit is helpful to determine cost since a BDA may consist of 5 or more BDA units in order to completely span the channel. Construction of a BDA To complete the construction of a BDA, 2-4” wood posts will be spaced approximately 2’ apart and positioned in a U shape, with the bend of the U located on the downstream side (See Figure 1). The number of posts needed will vary depending on the width of the creek. The BDA should span the entire creek width from one bank of the creek to the other. On larger creeks, it will require more posts to span the entire creek. 2’ of woven willow branches must be stacked on top of each other to form the dam wall. These branches should span the entire dam and go onto the sides of the bank. If willow branches are not available, other approved localized tree branch materials may be used, such as pinyon and juniper branches. These should be laid across the entire width of the BDA to create the dam wall and should be 2’ tall above the streambed and approximately 2’ thick so that it prevents water from flowing through the dam. A section of biodegradable coconut fiber approximately 4’ in width should be attached to the top of the BDA and span the length of the entire BDA. The one edge should be placed on the top of the dam wall and pushed tight against it. While the remaining material should be laid along the stream bottom so as to capture all material and prevent water from undercutting the dam and instead push water over the top of the dam. This will help catch sediment and prevent water from undercutting and flowing below the BDA. Lastly, for the BDA to be considered complete, mud, rocks, and litter should be placed to plug holes and allow water to build up behind the dam and flow over the top center of the dam, rather than underneath or the sides. Water should not be flowing around the sides or underneath the BDA. It does not need to be completely blocked off from leaking through the dam but a majority of the flow should be pouring over the center top. To encourage water to flow down the center of the dam an not around the sides; the sides should be slightly taller than the middle. Once all of this is complete, the BDA is finished. Once the BDA is finished, you can count how many BDA units it took to complete it. For example, if a BDA has 5 posts spaced two feet apart and all the other materials are in place than you would have 5 BDA units. Most BDAs in this contract will have 5 BDA units. Because of the variability in stream width and the number of BDA units needed to construct a BDA, the bids will be based on BDA units and not total BDAs constructed. The contract will be bid on a per BDA unit basis. The lowest cost per BDA unit will be awarded the contract.
